Law of Fatigue Limit : Part I. Condition of Fatigue Endurance Limit, and Relations between Various Endurance Limits

Abstract

A new criterion is proposed. It is considered that the fatigue failure occurs in two stages ; the fatigue under cyclic shearing stress and the failure under normal tensile stress. Strength of the material is reduced by fatigue, and this reduction of tensile strength across a certain plane is considered, when the fatigue is saturated, to be proportional to the component of the cyclic shearing stress on that plane. As to the failure, the law of failure will be quite similar to that under static stress, of course the effect of stress distribution being taken into account. Fatigue limits under cyclic tension-compression, cyclic torsion and rotating bending were respectively calculated from the above hypothesis. The ratio of the limit under torsion to that under bending conforms closely with experiments. The ratio of the limit under tension-compression to that under bending also conforms closely with some experiments. But in some other cases they do not conform. In this respect further studies will be necessary.